Method and apparatus for a floating reference electric field sensor

Abstract

Method and apparatus for sensing electric fields with a dipole antenna, wherein the antenna generates an antenna signal representative of electric field potential, includes a signal generator for generating mixing signals having known characteristics, variable capacitors for generating first output signals representative of the antenna signal, wherein the capacitance of the variable capacitors is varied by the mixing signals such that the antenna signal is frequency translated. A signal processor processes the first output signals to generate a second output signal representative of the electric field. In a preferred embodiment of the invention, the mixing signals are a quadrature pair of sine waves. In an especially preferred embodiment, the variable capacitors are each a frame, a speaker mounted to the frame. The speaker cones move in response to a signal applied to each speaker. A first plate is attached to the cone and a second plate is attached to the frame, wherein movement of the cone moves the first plate relative to the second plate. In a still further embodiment, an isolation member is provided to generate a third output signal which is isolated from one half of the dipole, i.e., the floating antenna reference. In such embodiment the antenna effective length variation, due to different measurement devices adding varying conductor lengths to the ground reference, is minimized. It is preferred for the isolation member to be an optical isolator.

What is claimed is: 
     
       1. Apparatus for sensing electric field gradients, said apparatus comprising: an antenna for measuring the potential between two points in an electric field to produce an antenna signal representative of a gradient of said electric field;   signal generator means for generating mixing signals having known characteristics;   variable capacitor means, connected to receive said antenna signal and said mixing signals, for generating first output signals representative of said antenna signal, wherein the capacitance of said variable capacitor means is varied by said mixing signals such that said antenna signal is frequency translated; and   signal processing means, connected to receive said first output signals, for processing said first output signals to generate a second output signal representative of the electric field gradient sensed by said antenna.   
     
     
       2. The apparatus of claim 1, wherein said mixing signals comprise a quadrature pair of sine waves. 
     
     
       3. The apparatus of claim 2, wherein said first and second variable capacitors each comprise a frame, a speaker mounted to said frame, said speaker comprising a cone which moves in response to a signal applied to said speaker, a first plate attached to said cone and a second plate attached to said frame, wherein movement of said cone moves said first plate relative to said second plate. 
     
     
       4. The apparatus of claim 3, wherein said first and second plates are circular. 
     
     
       5. The apparatus of claim 3, wherein said first and second plates are attached to said cone and said frame so that said first and second plates are substantially parallel. 
     
     
       6. The apparatus of claim 5, wherein said first and second plates are spaced approximately 7 mm apart. 
     
     
       7. The apparatus of claim 1, wherein said variable capacitor means comprises first and second variable capacitors, wherein said mixing signals comprise quadrature pair signals wherein one of said quadrature pair signals is connected to said first variable capacitor and wherein another one of said quadrature pair signals is connected to said second variable capacitor. 
     
     
       8. The apparatus of claim 7, wherein said antenna signal is provided to said first plate and wherein said second output signal is generated from said second plate. 
     
     
       9. The apparatus of claim 1, wherein said antenna comprises first and second halves, wherein said first half generates said antenna signal and said second half is connected to a floating reference, said apparatus further comprising: isolation means, connected to receive said second output signal, for generating a third output signal, wherein said third output signal is isolated from said floating reference.   
     
     
       10. Apparatus for sensing electric field gradients, said apparatus comprising: an antenna for measuring the potential in an electric field to produce an antenna signal representative of a gradient of said electric field, wherein said antenna comprises a first and second halves, wherein said first half generates said antenna signal and said second half is connected to a ground reference;   signal processing means for processing said antenna signal to generate an output signal representative of the electric field sensed by said antenna; and   isolation means, connected to receive said antenna signal and connected to said signal processing means, for electrically isolating said signal processing means from said ground reference, whereby variation of effective antenna length is minimized.   
     
     
       11. The apparatus of claim 10, wherein said isolation means comprises an optical isolator. 
     
     
       12. A method for sensing electric field gradients, said method comprising the steps of: providing an antenna and measuring the potential between two points in an electric field to produce an antenna signal representative of a gradient of said electric field;   generating mixing signals having known characteristics;   providing variable capacitors, each connected to receive said antenna signal;   generating first output signals, representative of said antenna signal, by varying the capacitance of said variable capacitors in response to said mixing signals such that said antenna signal is frequency translated; and   processing said first output signals to generate a second output signal representative of the electric field gradient sensed by said antenna.   
     
     
       13. The method of claim 12, wherein said step of generating mixing signals comprise the step of generating a quadrature pair of sine waves. 
     
     
       14. The method of claim 12, wherein said step of providing variable capacitors comprises the steps of providing first and second speakers, mounting said first and second speakers to a frame, each of said first and second speakers comprising a cone which moves in response to a signal applied to said speaker, attaching a first plate to said cone and attaching a second plate to said frame, wherein movement of said cone moves said first plate relative to said second plate. 
     
     
       15. The method of claim 14, wherein said steps of attaching first and second plates comprises attaching said first and second plates so that said first and second plates are substantially parallel. 
     
     
       16. The method of claim 15, wherein said steps of attaching said first and second plates further comprises spacing said first and second plates approximately 7 mm apart. 
     
     
       17. The method of claim apparatus of claim 14, wherein said step of providing variable capacitors, each connected to receive said antenna signal, comprises the step of providing said antenna signal to said first plate and wherein said second output signal is generated from said second plate. 
     
     
       18. The method of claim 12, wherein said antenna comprises first and second halves, wherein said first half generates said antenna signal and said second half is connected to a floating ground reference, said method further comprising the step of isolating said second output signal from said ground reference by generating a third output signal isolated from said floating ground reference. 
     
     
       19. A method for sensing electric field gradients, said apparatus comprising: an antenna for measuring the potential in an electric field to produce an antenna signal representative of a gradient of said electric field, wherein said antenna comprises first and second halves, wherein said first half generates said antenna signal and said second half is connected to a ground reference;   providing signal processing means for processing said antenna signal to generate an output signal representative of the electric field sensed by said antenna; and   electrically isolating said signal processing means from said ground reference, whereby effective antenna length of said antenna is minimized.   
     
     
       20. The method of claim 19, wherein said step of electrically isolating said processing means comprises the step of optically isolating said processing means from said ground reference.